The Post Groundhog Day Storm of 2009

Friday 11:45 AM

The title sounds ominous, doesn't it? I use a title like that in one of my forecaster training sessions where a storm looked good on paper (seemingly deserving grandiose attention) days in advance but in the end did not have a big impact on the weather where first expected. Yesterday, the GFS operational run, the ECMWF and other models all showed a substantial storm sweeping northward or north-northeastward through the eastern part of the country. Heavy rain was shown near and east of the storm track with heavy snow to the west. Since then, most models have trended eastward.

We have seen that before. In fact, last week the GFS had this week's storm going exactly where it wound up. However, a couple of days later it trended south and east, and that raised hopes for snow in the Middle Atlantic states. Then, however, once the storm started taking shape, models trended back to the original west of the Appalachians track. Will that happen again? I don't know. On argument for that is that the late weekend warm-up in the East will put the region on the warm side of a front that only slowly moves through the Great Lakes and Ohio Valley. It would be natural for a storm to follow that front, taking a track over or west of the mountains. On the other hand, we don't see any big high pressure area to the north of this storm, so all the strengthening is supposed to come from a still unproven upper air short wave that will plunge toward the Gulf states this weekend. If the resulting storm is slow to develop, the whole thing may just be like a cold front for the Appalachians and perhaps much of the Middle Atlantic region. The storm would not take shape until it out to sea, and might then only hit eastern New England with a lot of precipitation and wind. On the video, when I look at the ensemble forecasts from last night, you will see one solution that looks just like that (in fact, it suggests no major storm anywhere in the East). However, the same ensemble set includes members that look ominously stormy for a many places.

Henry Margusity may or may not include this in his story, but he mentioned a data factor that could impact the computer models (but we have not verified this is the case today). There is a big volcano erupting in Alaska, and planes are probably being re-routed to avoid the plume of ash, etc. that can damage engines, etc. Those aircraft are equipped with weather monitoring instruments, and that data is very useful in regions where other types of data are not available. (The area affected is in or near the area where a lot of the traffic flies between Asia and North America. If the the weather system that will either cause or prevent the alleged storm for next week is over an area with poor data now, the numerical models have no way to handle it properly.

For now, we need to consider many options but commit to none other than the pledge to work hard this weekend to figure it out. The easiest parts of the forecast include the cold day we'll have in the Northeast tomorrow, the warm-up Sunday into Monday, then the cold weather following whatever happens Tuesday. In the short term we are dealing with a cold trough aloft coming through the East and triggering clumps and bands of snow showers, some of which have been producing short bursts of snow. In past episodes like this, there have been chain-reaction collisions when cars and trucks suddenly encounter a band of heavy snow with bad visibility.